Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$132.88	8.506%	$144.1828	$144.18	$144.20	$144.20
Purchase #2	$190.90	10.419%	$210.7899	$210.79	$210.80	$210.80
Purchase #3	$190.89	3.382%	$197.3459	$197.35	$197.35	$197.30
Purchase #4	$167.80	10.695%	$185.7462	$185.75	$185.75	$185.70
Purchase #5	$39.75	10.123%	$43.7739	$43.77	$43.75	$43.80
Purchase #6	$86.35	5.697%	$91.2694	$91.27	$91.25	$91.30
Purchase #7	$208.88	5.505%	$220.3788	$220.38	$220.40	$220.40
7 purchase totals =	$1,017.45		$1,093.4869	$1,093.49	$1,093.50	$1,093.50